Mattis told his fellow members of the military in a letter that “our department is proven to be at its best when the times are most difficult.”

“It has been my high honor to serve at your side. May God hold you safe on the air, on land, and at sea,” Mattis wrote.

Mattis farewell message: “Our Department is proven to be at its best when the times are most difficult. So keep the faith in our country and hold fast, alongside our allies, aligned against our foes.” pic.twitter.com/YuxnfkutGg

I am pleased to announce that our very talented Deputy Secretary of Defense, Patrick Shanahan, will assume the title of Acting Secretary of Defense starting January 1, 2019. Patrick has a long list of accomplishments while serving as Deputy, & previously Boeing. He will be great!

Mattis’ resignation letter was seen as rebuke to Trump’s foreign policy objectives. “[Y]ou have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects,” he wrote.

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